Electrode and method

ABSTRACT

An electrode for use in electrometallurgical applications is in the form of a composite sheet comprising a copper inner layer, a refractory metal outer layer on each side of said copper layer, said outer layers being substantially coextensive and extending beyond the edges of said copper layer, in at least that portion of the electrode subject to anodic attack, to form a channel defined by the edges of said copper layer and the portions of outer layers extending beyond the edges of the copper layer, and a refractory valve metal in said channel and the method of making such electrode, said refractory valve metal having a lower melting point than said refractory metal outer layers.

United States Patent 1 Grunig l l ELECTRODE AND METHOD [75} lm cntor:James K. Grunig. Tucson. Ariz.

[73} Assignee: The Anaconda Company. New

\ ork, NY

OTHER PUBLlCATlONS Defensive Publication 689.485. March 1969, 8M]

45] Apr. 1,1975

Primary liruminer-F. C. Edmundson Attorney, Agent. or Firm-Pennie &Edmonds [57 l ABSTRACT An electrode for use in electrometallurgicalapplications is in the form of a composite sheet comprising a copperinner layer. a refractory metal outer layer on each side of said copperlayer. said outer layers being substantially coextensive and extendingbeyond the edges of said copper layer, in at least that portion of theelectrode subject to anodic attack, to form a channel defined by theedges of said copper layer and the portions of outer layers extendingbeyond the edges of the copper layen and a refractory valve metal insaid channel and the method of making such electrode. said refractoryvalve metal having a lower melting point than said refractory metalouter layers.

5 Claims 5 Drawing Figures ELECTRODE AND METHOD BACKGROUND OF THEINVENTION At present. there are a variety of electrodes used inelectrometallurgieal applications. In order to extend electrode life.there are now under development composite sheet materials for supportingelectrically active materials used as anodes. for example, inelectrowinning procedures. Typically. such sheet materials consist of asheet of copper covered by sheets of a refractory metal for example. avalve metal such as tantalum or columhium. A valve metal is a metalwhich forms an electrically nonconducting film on its surface whenoxidized. The principal refractory valve metals are titanium. zirconium.hafnium, columbium. tantalum. molybdenum, and tungsten.

These composite sheets are ordinarily from about 0.05 to 0.09 inch thickand are produced by layering together thicker sheets of the metalsrolling the combined sheets to the desired thickness. and shearing thethus formed composite sheet to size. After shearing the composite sheethas an exposed surface of copper all about the edges thereof which wouldhe attacked electrochemically upon use if not protected. As aconsequence. a variety of methods have been tried. none entirelysatisfactory, in an effort to protect the copper edge from attack. Onemethod has been to coat the exposed copper edge with a non-conductivematerial, but this has not proven satisfactory since such coatings havebeen subject to chemical attack and are rapidly removed from theelectrode during use leaving the copper exposed.

SUMMARY OF THE INVENTION The present invention provides a compositesheet electrode which is rapidly and easily fabricated and whichprotects the copper edges against electromechanical and chemical attack.

Briefly stated, the present invention comprises an electrode for use inelectromctallurgical applications comprising a composite sheetcomprising a copper inner layer. a refractory metal. which may withadvantage be a valve metal. outer layer on each side of said copperlayer. said outer layers being substantially coextensive and extendingbeyond the edges of said copper layer. in at least that portion of theelectrode subject to anodic attack. to form a channel defined by theedges ofsaid copper layer and the portions of outer layers extendingbeyond the edges of the copper layer. and a refractory valve metal insaid channel. said refractory valve metal having a lower melting pointthan said refractory metal outer layers. The invention also comprisesthe method of making such electrode comprising forming a composite sheetof desired thickness comprising a copper inner layer and a refractorymetal outer layer on each side of said copper layer and having anexposed edge of copper. removing a portion of the copper edge to form achannel between the new copper edge and the portions of said outerlayers extending beyond said new copper edge. and sealing said channelwith a refractory valve metal of lower melting point than the refractorymetal forming the outer layers.

DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a compositematerial electrode after shearing having an exposed copper surface;

FIG. 2 is a transverse cross-sectional view of the electrode taken alongline 2-2 of FIG. 1;

FIG. 3 is a view similar to FIG. 2 showing a portion of the copper edgelayer removed leaving a channel about the edge of the electrode;

FIG. 4 is an enlarged fragmentary view of one portion of the electrodeof FIG. 3 showing an electrically and chemically impermeable material insaid channel; and

FIG. 5 is a view similar to FIG. 4 showing the impermeable materialfilling the channel.

DETAILED DESCRIPTION Referring to the drawings, there is shown anelectrode I0 comprising an inner copper layer 11 and outer refractorymetal layers 12 and [3. The shape of the electrode can be varied widelyand does not form any part of the instant invention. As discussed above.the composite electrode is formed by placing sheets of a refractorymetal about a central copper layer and rolling the combined sheets tothe desired thickness. The combined sheets are then sheared to theproper size and shape desired for the final electrode. as depicted inFIG. I, leaving an exposed copper edge I4.

In carrying out this invention, it is necessary that the copper edge 14shown in FIGS. 1 and 2 be preferentially removed as by chemical orelectromechanical etching or mechanical milling. The chemical etchingcan be-accomplished using any of the conventional materials. such asacids, which will attack copper but not the refractory material. In likemanner. the electromechanical etching can be accomplished using currentsand solutions known to preferentially remove the copper withoutattacking the refractory metal. Mechanical milling can be accomplishedby use of an abrasive wheel whose diameter or thickness is such that itwill fit between the refractory metal layers 12 and 13 to selectivelyabrade and remove only the copper. It is preferred to remove the copperto a depth about equal to the thickness of the copper layer. FIG. 3illustrates the electrode after the copper removal and shows channel 15formed by the new copper edge 16 and the portions of the outer layers 12and 13 which extend beyond the copper edge 16. The channel need only beformed along that portion of the electrode that is to be subjected toanodic attack.

After the preferential removal of copper has been accomplished. arefractory valve metal of lower melting point than the refractory metalof the outer layers 12 and I3 is placed in the channel 15. As best shownin FIG. 4, a strand or wire 17 of impermeable material is placed in thechannel 15. The use ofa wire is preferred. although other forms of thematerial can also be used. The dimensions of the wire are such that whentreated as hereinafter discussed, it will be sufficient to seal thechannel IS and completely cover the exposed new edge 16 of the copper.The low melting valve metal is heated so as to melt the same and formthe seal 18 as depicted in FIG. 5. Conventional arc welding techniquesunder an inert atmosphere, such as argon. with either consumable ornon-consumable electrodes. are used to melt the material. Thetemperature used is that suffcient to melt the material 17, but notsufficient to advcrsely affect the refractory metal outer layers 12 and13. By heating under argon, it is possible also to avoid the formationof any brittle alloys of the impermeable material. The result is astrong seal 18 which completely covers the copper. However, other knownheating methods, such as ion bombardment, ultrasonic energy heating, andlaser heating, may be used to melt the wire.

As to materials, the refractory metal outer layer is preferably eithercolumbium or tantalum, although any of the other usual refractory metalsused in making composite electrodes can be utilized. Copper is thepreferred core or inner layer. With respect to the refractory valvemetal used in forming the seal, it is preferred to use a refractoryvalve metal which has a melting point substantially below the meltingpoint of the material of the refractory metal outer layers. A preferredmaterial for use to create a seal in accordance with this invention istitanium, which melts some 800C. below columbium and some l328C. belowtantalum, both of which may be used as a material of the outer layer.

Other metals which are electrically or chemically impermeable whensubjectcd to anodic attack can also be used. Other combinations ofrefractory valve metals include columbium to seal tantalum, columbium toseal tungsten, and tantalum to seal tungsten. ln each of these lattercombinations the material of the seal has a melting point substantiallybelow the melting point of the material of the outer layers.

Because the melting point of the refractory valve metals are generallyabove copper a means of melting the valve metal must be used which is asufficiently intense source of heat to melt the lower melting valvemetal completely while melting only an inconsequential amount of copper.

The thickness of the inner copper layer and the refractory outer layerscan vary widely, but it is preferred to have a composite in which theinner copper layer is from about 0.05 to 0.08 inch thick, and the outerrefractory metal layers from about 0.00l to 0.005 inch thick.

While the invention has been described in connection with a preferredembodimebt, it is not intended to limit the invention to the particularform set forth, but, on the contrary, it is intended to cover suchalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.

What is claimed is;

I. An electrode for use in electrometallurgical applications comprisinga copper layer, a pair of refractory metal layers, said refractory metallayers being formed of like material and disposed in juxtaposed relationon opposite sides of said copper layer, said refractory metal layersforming outer layers of said electrode, said outer layers beingcoextensive one with the other and at least with said copper layer inthose portions of said electrode not subject to anodic attack andextending beyond said copper layer in those portions of said electrodesubject to anodic attack to define a channel outlined by an edge of saidcopper layer and extending portions of said outer layers, and means insaid channel for sealing said copper layer in said portions of saidelectrode, said sealing means formed by a refractory valve metal havinga melting point between that of the material of said copper layer andouter layers and sub stantially below that of the outer layers.

2. The electrode of claim I wherein the refractory metal outer layer isselected from tantalum and columbium and the refractory valve metal istitanium.

3. The electrode of claim 1 wherein said copper layer has a thickness ofabout 0.05 to 0.08 inch and said outer layers each have a thickness ofabout 0.00] to 0.005 inch.

4. The electrode of claim 1 wherein the channel depth is substantiallyequal to the thickness of said copper layer.

5. The electrode of claim 4 wherein said refractory metal outer layer iscolumbium having a thickness of about 0.001 to 0.005 inch, said copperlayer has a thickness of about 0.05 to 0.08 inch, and the refractoryvalve metal is titanium.

1. AN ELECTRODE FOR USE IN ELECTROMETALLURGICAL APPLICATIONS COMPRISINGA COPPER LAYER, A PAIR OF REFRACTORY METAL LAYERS, SAID REFRACTORY METALLAYERS BEING FORMED OF LIKE MATERIAL AND DISPOSED IN JUXAPOSED RELATIONON OPPOSITE SIDES OF SAID COPPER LAYER, SAID REFRACTORY METAL LAYERSFORMING OUTER LAYERS OF SAID ELECTRODE, SAID OUTER LAYERS BEINGCOEXTENSIVE ONE WITH THE OTHER AND AT LEAST WITH SAID COPPER LAYER INTHOSE PORTIONS OF SAID ELECTRODE NOT SUBJECT TO ANODIC ATTACK ANDEXTENDING BEYOND SAID COPPER LAYER IN THOSE PORTIONS OF SAID ELECTRODESUBJECT TO ANODIC ATTACK TO DEFINE A CHANNEL OUTLINED BY AN EDGE OF SAIDCOPPER LAYER AND EXTENDING PORTIONS OF SAID OUTER LAYERS, AND MEANS INSAID CHANNEL FOR SEALING SAID COPPER LAYER IN SAID PORTIONS OF SAIDELECTRODE, SAID SEALING MEANS FORMED BY A REFRACTORY VALVE METAL HAVINGA MELTING POINT BETWEEN THAT OF THE MATERIAL OF SAID COPPER LAYER ANDOUTER LAYERS AND SUBSTANTIALLY BELOW THAT OF THE OUTER LAYERS.
 2. Theelectrode of claim 1 wherein the refractory metal outer layer isselected from tantalum and columbium and the refractory valve metal istitanium.
 3. The electrode of claim 1 wherein said copper layer has athickness of about 0.05 to 0.08 inch and said outer layers each have athickness of about 0.001 to 0.005 inch.
 4. The electrode of claim 1wherein the channel depth is substantially equal to the thickness ofsaid copper layer.
 5. The electrode of claim 4 wherein said refractorymetal outer layer is columbium having a thickness of about 0.001 to0.005 inch, said copper layer has a thickness of about 0.05 to 0.08inch, and the refractory valve metal is titanium.